The objective of this Phase II project is to develop a more effective tool for assessing the development potential of human oocytes and to reduce the emotional, health, and financial costs of low IVF success rates, presently approximately 25% per cycle. To compensate for these low rates, as many as three or more embryos are transferred to the mother-this practice is a leading cause of multiple and often premature births. Low success rates also lead to multiple, emotionally draining and expensive interventions. An ability to select high quality oocytes is critical to achieving successful outcomes. The main premise of this application is that reliable quantitative analysis of oocyte structures can improve IVF techniques, and proposes to apply to this task a new type of microscope that measures birefringence, an optical property exhibited in many cellular structural elements. Compared to images provided by traditional Hoffman or DIG optics presently used for oocyte assessment, non-invasive birefringence imaging using CRI's unique liquid crystal polarized light microscope dramatically and quantitatively highlights the meiotic spindle and other cellular structures by measuring birefringence retardation at each image point in the field of view. Phase I demonstrated that birefringence imaging of oocyte structures provides information that correlates significantly with embryo development and, ultimately, clinical outcome. Spindle visualization was also shown to be useful in assessing viability of cryopreserved oocytes, another critical and otherwise unsolved problem. Phase II specific aims include extending functionality to allow quantitative measurement of birefringence in three dimensions, adding features to make operation more suitable to the clinical IVF setting, developing an appropriately sized and treated glass-bottom dish, developing software tools and algorithms that extract additional quantitative information about viability and condition, and working with three beta-sites to test systems and provide vital feedback on effectiveness and operation.